The field of the invention is two-dimensional bolometer arrays, and particularly to non-uniformity correction thereof.
Two-dimensional arrays of bolometers require high electrical uniformity to permit efficient electrical readout of signals. Non-uniformities may be due to fabrication irregularities in any part of the array, eg. in the sensors themselves, in any blocking diodes in the array, or in the bus lines. High uniformity is difficult to attain during manufacture. This invention allows high uniformity to be attained by an electronic correction circuit, which automatically corrects for non-uniformity in the array. Two types of circuits are shown, with different merits. In the pior art such as U.S. Pat. Nos. 3,562,418, 3,668,408 and 3,676,590 are shown two-dimensional matrix arrays of photoresponsive elements.
A two-dimensional bolometer array such as is used in the present invention is made up of a number of resistive thermal detectors. A resistive thermal detector is one whose electrical resistance changes as a function of temperature. Such two-dimensional arrays are known.
In the prior art, such as U.S. Pat. No. 3,801,949 there has been taught a radiation detecting solidstate imaging device which is small in size and which has a two-dimensional array of thermal detectors in an integrated microcircuit. The detector array is fabricated on a single crystal silicon substrate coated with a thin layer of electrical insulating material, such as silicon dioxide or silicon nitride. Etched openings are made in the silicon beneath the insulating layer wherever a sensing element is desired for the purpose of thermally isolating the sensing elements from their surroundings.
Another prior art example of thermal sensors on the crystalline structure of a single crystal semiconductor is the Johnson and Higashi U.S. Pat. No. 4,472,239, assigned to the same assignee as the present invention. The referenced patents shows that the technique is known to manufacture micromechanical devices by etching into single crystal silicon. The citation of these two patents is provided merely as background and is not deemed as prior art to the specific invention claimed in this application.